Thames Water Final Water Resources Management Plan 2019 Technical Appendices Appendix D: Water resource zone integrity Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 Table of contents A. Introduction 1 B. WRZ description 3 London ......................................................................................................................................... 3 Swindon and Oxfordshire............................................................................................................. 4 Slough, Wycombe and Aylesbury ................................................................................................ 5 Kennet Valley ............................................................................................................................... 6 Guildford ....................................................................................................................................... 7 Henley .......................................................................................................................................... 8 C. Integrity assessment process 9 Figures Figure D-1: Principal features of the London WRZ.................................................................................. 3 Figure D-2: Principal features of the SWOX WRZ................................................................................... 4 Figure D-3: Principal features of the SWA WRZ ..................................................................................... 5 Figure D-4: Principal features of the Kennet Valley WRZ ....................................................................... 6 Figure D-5: Principal features of the Guildford WRZ ............................................................................... 7 Figure D-6: Principal features of the Henley WRZ .................................................................................. 8 Figure D-7: WRZ integrity process diagram ............................................................................................ 9 Tables Table D-1: Identified WRZ sub-areas with property numbers ............................................................... 10 Table D-2: WRZ integrity proforma ........................................................................................................ 11 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 Water resource zone integrity • In this appendix we present our assessment of the integrity of our Water Resource Zones (WRZs), the building blocks of a Water Resources Management Plan (WRMP). • Our WRZ boundaries are unchanged from WRMP14. • In the Swindon and Oxfordshire (SWOX) and Kennet Valley WRZs, areas of isolated supply do exist. However, they are relatively small and around the de-minimis threshold and suitable contingency plans are in place should the supply infrastructure fail. • Guildford WRZ is made up of two distinct sub-areas that are above the de-minimis threshold. However, our assessment is that the supply demand situation is sufficient that customers in both areas share the same level of service. Options to improve the interconnectivity are known but not required at the present time. • WRZ integrity will continue to be reviewed on a routine basis. A. Introduction D.1 A WRMP is built up of assessments undertaken at the WRZ level. A WRZ provides a water company with a strategic framework for managing water resources supply and demand management and investment. D.2 The WRZ describes an area within which the management of supply and demand is largely self-contained (apart from agreed bulk transfers of water). Within the WRZ, supply infrastructure and demand centres are generally integrated to the extent that customers in the WRZ experience the same risk of supply failure. Consequently, all customers share the same level of service. There will be limitations in achieving these requirements within a distribution network but significant numbers of customers should not experience different risks of supply failure within a single WRZ. D.3 The Water Resource Planning Guidelines (WRPG)1 definition of a WRZ is: "The largest possible zone in which all resources, including external transfers, can be shared and, hence, the zone in which all customers will experience the same risk of supply failure from a resource shortfall." 1 Environment Agency and Natural Resources Wales produced in collaboration with Defra, the Welsh Government, and Ofwat, Water Resources Planning Guideline: Interim update, April 2017 1 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 D.4 The Thames Water supply area comprises six WRZs: London; SWOX; Henley; Kennet Valley; Slough, Wycombe and Aylesbury (SWA); and Guildford (Section 1: Introduction and Background) D.5 Following assessment and discussion with the Environment Agency, it has been agreed that our WRZ boundaries were suitable for use in the draft WRMP19 and are in keeping with the above definition. D.6 The remainder of this appendix is structured as follows: • A description of each WRZ • The WRZ integrity process 2 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 B. WRZ description London D.7 The London WRZ is supplied primarily (80%) from surface water resources of the River Thames and River Lee, either directly or via storage reservoirs. The remainder of the supply is made up of groundwater abstractions, particularly from the chalk aquifer under south east London. We are also able to abstract and treat brackish estuarine water at our desalination plant at Beckton. D.8 The water is transported to water treatment works and then treated water is conveyed to an integrated distribution system, a key feature of which is the Thames Water Ring Main (TWRM). This is a large diameter pipe that runs underneath central London and connects the Thames and Lee systems and allows us to supply the London WRZ flexibly. D.9 London is a net exporter of water, with large bulk supplies provided to Essex and Suffolk Water and Affinity Water (Section 4: Current and future water supply). Figure D-1: Principal features of the London WRZ Export to Affinity Water Lee Valley Reservoirs Export to Essex and Suffolk Water Ring Main South East London Groundwater Thames Valley Reservoirs 3 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 Swindon and Oxfordshire D.10 The SWOX WRZ is supplied primarily from groundwater (60%), supported by surface water abstractions and the Oxfordshire reservoir, near Oxford. A number of distribution improvements have been made in recent years and the main movement of treated water is northwards and westwards. Key sources and distribution are as follows: • The ‘Gatox’ mains transfer water from the chalk in the Goring Gap towards Oxford and Swindon • Oxfordshire reservoir provides water north to Bicester and Banbury and west to Swindon • The Oolites of the Cotswolds serve the local demand to the west of the WRZ • Chalk groundwater serves the Upper Kennet Valley • Water is received from the SWA WRZ to serve local demands on the eastern border D.11 At the extremities of the zone there remain areas with isolated networks i.e. they are not connected into the wider distribution network. These areas are often rural and have needed relatively little investment to balance supply and demand. Figure D-2: Principal features of the SWOX WRZ Cotswold Groundwater Oxfordshire Import Reservoir from SWA Goring Gap Groundwater Upper Kennet Groundwater – 4 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 Slough, Wycombe and Aylesbury D.12 The SWA WRZ is supplied entirely from groundwater. There are no raw water reservoirs. The vast majority of the supply is from Thames-side groundwater to the south of the zone, the distribution system then transfers the water to Windsor and north to Aylesbury through Slough and Wycombe via large ‘Mid Bucks’ mains. D.13 The zone supports a regular transfer to SWOX in the west of the zone. Figure D-3: Principal features of the SWA WRZ Export to SWOX Thames-side Groundwater 5 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity – April 2020 Kennet Valley D.14 The Kennet Valley zone is primarily supplied from groundwater (60%) supported by a surface water abstraction from the River Kennet at Lower Kennet water treatment works. There are no raw water reservoirs. D.15 The zone does not cover the whole of the catchment of the River Kennet. The upper Kennet, upstream of Hungerford, is part of the SWOX WRZ which historically has developed to serve the needs of the local area and to support the growth in Swindon. D.16 The Kennet Valley WRZ is primarily made up of two large sub-areas (Reading and Newbury) and smaller island zones. Connections between the sub-area and island zones are limited. D.17 There is minor interconnectivity with both South East Water and Southern Water to the south and east of the zone. There are also connections to Henley and SWOX, but no water is transferred under normal operation. Figure D-4: Principal features of the Kennet Valley WRZ Playhatch island zone Burnt Hill island zone Mid Kennet Groundwater Sub- area Groundwater Sub- area Hungerford island zone d Lower Kennet Fobney Groundwater LowerWTW Kennet Groundwater WTW – 6 Final Water Resources Management Plan 2019 Appendix D: Water resource zone integrity